As transportation devices and technologies have evolved, urban areas have increased in size and population and knowledge regarding areas over which transportation might be desirable, cognitive tasks associated with transportation have also increased in complexity. Further, the nature, complexity and degree of the risks to a traveler or bystander have increased as other aspects of transportation have become more sophisticated.
At one time, natural hazards, such as predators, weather-related phenomena and topographical features (e.g., cliffs, waterfalls etc.) were the issues associated with travel, and these were relatively comprehensible, predictable (to a degree) and could be planned for, watched for and appropriately addressed to some extent. However, with the advent of machine-powered travel, the nature of the risks, their unpredictability, the magnitude of potential disaster and the rapidity with which events are capable of unfolding have all increased. Increasing population densities in many areas further compound the difficulties of vehicular travel, through multiple factors, including congestion, lack of visibility and increased travel velocities.